The present invention relates to the abatement of gaseous effluents created during semiconductor substrate processing. More specifically, the present invention relates to a method and apparatus for reducing effluent levels in the gaseous discharge of semiconductor substrate processing equipment by using ozone in the abatement process.
In recent years, the release of certain gaseous chemical compounds into the environment has become the subject of various laws and regulations administered by regulatory agencies such as the Environmental Protection Agency (EPA). Many of these compounds are monitored by agencies such as the EPA for potentially harmful effects on the environment.
The semiconductor industry is particularly affected by these concerns because of the numerous kinds of chemicals involved in the fabrication of integrated circuits. The release of chlorofluorocarbons (CFCs) and perfluorinated compounds such as CF.sub.4, C.sub.2 F.sub.6 and NF.sub.3 (also called perfluorocarbons, or PFCs), which are used in semiconductor processing operations such as thin film etching, chemical vapor deposition (CVD) and the cleaning of processing chambers, among other operations, is regulated by the EPA. Also regulated is the release of nitrogen oxide (NO.sub.X) compounds, which may be emitted by certain semiconductor processing systems.
Illustrated in FIG. 1 is a substrate processing system 100 of the prior art capable of carrying out one or more processes that may discharge such effluent gases, such as CFCs, PFCs, nitrogen oxides and ozone (e.g., a CVD system). The process gases required for the process being performed are introduced into a processing chamber 105 via process gas lines 110(1)-(M). These process gases are then energized (e.g., thermally or by radio-frequency (RF) energy), to promote reactions that form the desired layer(s) on one or more substrates (not shown) disposed within processing chamber 105. The CFCs, PFCs, nitrogen oxides and other effluent gases generated by these reactions, along with unreacted portions of the process gases, are removed from processing chamber 105 by a vacuum pump (not shown) and are exhausted through effluent line 120 into an abatement device 130. Optionally, one or more combustion fuels may be introduced into a combustion chamber (not shown) of abatement device 130 via combustion fuel lines 140(1)-(N). In the combustion chamber, chemical reactions occur between the effluent gases and optional combustion fuels.
One technique commonly used in the abatement of effluent gases is thermal abatement. Thermal abatement devices use thermal energy sources such as an open flame or electric arc to promote the chemical reactions that convert the undesirable compounds into less volatile, environmentally safer compounds. If a thermal abatement technique is employed, various combustion fuels may be introduced into the combustion chamber along with the effluent gases to further promote the decomposition of undesirable compounds. Which combustion fuels are used, if any, depends on the abatement technique employed. Combustion fuels such as oxygen-containing gases (e.g., oxygen or air) and hydrogen are often employed due to their reactivity and the high heat produced by their reactions with each other and various effluent gases.
Another common abatement technique is the use of RF energy to dissociate compounds within the effluent gas stream. An example of this is a plasma technique in which a plasma is formed from effluent gases introduced into the combustion chamber. This ionization promotes decomposition of undesirable compounds within the effluent gases, converting them into safer, more tractable compounds.
Regardless of the abatement technique employed, energy is applied to the effluent gases and optional combustion fuels to promote combustion. The by-products of the abatement reactions are then exhausted along with any unreacted gases. Depending upon the configuration, more abatement operations may be performed to further reduce levels of undesirable compounds within the exhaust gases, using methods such as water scrubbing, catalysis and filtering. For example, FIG. 1 shows abatement device 130 connected to a water scrubber 150. In water scrubbing, effluent gases are brought into contact with water, using methods such as bubbling the effluent gases through the water, sending the effluent gases through a water spray or the like. Certain of the effluent gases then react with the water, forming inert or, at least, less hazardous compounds. Alternatively, the exhaust gases may be discharged directly into the atmosphere. However, regardless of the abatement technique employed, several types of compounds in an effluent gas stream may not be abated sufficiently using traditional techniques. This is particularly true of PFCs. Moreover, newer methods capable of abating these compounds such as plasma abatement are often expensive and require large amounts of energy.
As illustrated in FIG. 1, substrate processing system 100 may also include an ozone generator 160 that generates ozone (O.sub.3) for use in some substrate processing operations. For example, substrate processing system 100 might be capable of depositing a silicon oxide film (SiO.sub.X). Such a film may be deposited at atmospheric pressure and at a temperature as low as 250.degree. C. by reacting tetraethylorthosilicate (Si(C.sub.2 H.sub.5 O).sub.4), also called tetraethoxysilane (TEOS), with ozone. TEOS/ozone silicon oxide films are desirable because they exhibit smooth oxide profiles over steps, good filling of high aspect-ratio gaps (i.e., gaps with a high depth-to-width ratio) and desirable electrical characteristics. A TEOS/ozone process is suitable for depositing silicon oxide films for applications such as intermetal dielectrics. The thermal reaction that takes place between TEOS and ozone is given by: EQU Si(C.sub.2 H.sub.5 O).sub.4 +8O.sub.3 - - - &gt;SiO.sub.2 +10H.sub.2 O+8CO.sub.2
Ozone generator 160 may use any one of several ozone generation techniques. For example, ozone generator 160 might use an electric arc technique, generating ozone by passing an oxygen-containing gas through an electric arc. An example of an ozone generation system employing this method is AX8200A from Astex, Inc., of Woburn, Mass. Normally, in processes such as the TEOS/ozone process described above, ozone is generated continuously throughout operation of the chamber to maintain stable process parameters and flow rates, rather than simply shutting down ozone generator 160.
Thus, ozone is directed to processing chamber 105 when the process being performed requires ozone. However, when the process being performed does not require ozone or when a substrate is not being processed (e.g., while a substrate is being transferred into or out of the chamber or during the cleaning of processing chamber 105), a bypass valve 170 directs the unused ozone through a bypass line 180 that feeds into an ozone abatement device 190. Ozone abatement device 190 normally renders ozone inert by converting the ozone into oxygen. Such conversion methods include thermal abatement, ultraviolet (UV) catalysis (in which the ozone is photolytically decomposed) and chemical catalysis (in which ozone is chemically decomposed by reaction with a compound such as manganese dioxide (MnO.sub.2)).
As is evident from the above, it is desirable, from both a regulatory and an environmental perspective, to reduce or eliminate the effluents emitted by substrate processing equipment, such as CFCs, PFCs, nitrogen oxides and ozone. It is also desirable to provide more effective abatement of these compounds using the facilities already available in certain substrate processing systems. Moreover, it is desirable to increase abatement efficiency, in terms of power and fuel consumed in the abatement process.
Aside from its use in processing substrates, ozone has also found use in the abatement of various toxic or undesirable chemicals. For example, ozone has been employed in the destruction of certain chemical weapons, combining with the lethal chemical components to render them inert. Ozone has also been used to decontaminate soil containing solid or liquid wastes, when such wastes include organic contaminants amenable to photodegradation. However, ozone has not been used in the abatement of the effluent gases generated by substrate processing systems.